import java.util.*;
import java.util.Arrays;
//import java.sql.Date;
//import java.util.Date;
import static java.lang.Math.*;
import static java.lang.Math.sqrt;
//import static java.lang.System.out;




class Demo{
    public static int count = 100;

    public int func(){
        Demo demo1 = new Demo();
        Demo demo2 = new Demo();
        Demo demo3 = new Demo();
        demo1.count++;
        demo2.count++;
        demo3.count--;
        Demo.count++;
        return count;
    }

    public static String ret = "ceshi";
}


public class Test3 {


    public static void main(String[] args) {
        //Student3 s4 = new Student3("Wang" ,19);
        System.out.println(Student3.getClassRoom());

    }



    public static void main5(String[] args) {
        Demo demo = null;
        System.out.println(demo.ret);
    }



    public static void main4(String[] args) {
        Demo demo = new Demo();
        System.out.println(demo.func());
    }




   public static void main3(String[] args) {
//        Student3 s4 = new Student3("Wang" ,19);
//        Student3 s5 = new Student3("Jun" ,17);
//        Student3 s6 = new Student3("Kai" ,20);
//
//        System.out.println(s4.classRoom);
//        System.out.println(s5.classRoom);
//        System.out.println(s6.classRoom);

//       System.out.println(Student3.classRoom);
   }







    public static void main2(String[] args) {
        double x = 30;
        double y = 40;
       // double result = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
        double result = sqrt(pow(x, 2) + pow(y, 2));
        System.out.println(result);
    }




//    public static void main1(String[] args) {
//
//        Student3 s1 = new Student3();
//        //s1.name = "Karry";
//        s1.setName("Karry");
//        //s1.age = 25;
//        s1.setAge(19);
//        //s1.doClass();
//        out.println(s1.getName());
//        out.println(s1.getAge());
//
//
//        out.println("======================");
//
//        int[] arr = {1,2,3,4,5};
//        out.println(Arrays.toString(arr));
//
//        Date date = new Date();
//        //Date date1 = new Date();
//    }

}
